Due to some drawbacks of well logging instruments utilizing gamma ray sources and gamma ray detectors, development of well logging instruments that instead utilize x-ray generators and x-ray detectors is desirable. As explained in U.S. Pat. No. 7,668,293 to Wraight et al., assigned to the same assignee as the present disclosure, an x-ray generator may include an electron accelerator and a target. The electron accelerator accelerates electrons toward the target at a speed sufficient such that, when the electrons are stopped by the target (which is sufficiently thick such that it can stop all electrons striking it), x-ray photons are produced, for example by Bremsstrahlung radiation.
While advances in x-ray sources, x-ray detectors, and methods of analyzing the data generated thereby have been made, for example in U.S. Pat. No. 7,960,687 to Simon et al., U.S. Pat. No. 7,817,781 to Wraight et al., and U.S. Pat. No. 7,564,948 to Wraight et al., all of which are assigned to the same assignee as the present disclosure, the electron accelerators previously used suffer from some drawbacks. For example, commonly used cathodes in electron accelerators emit not only electrons, but also conductive particles. These conductive particles may build up on insulating surfaces inside the electron accelerator, thereby changing the characteristics of those insulating surfaces. This in turn may undesirably affect the electric field inside the electron accelerator, and therefore alter the focus point of the electron beam, which may result in the electron beam not striking the intended portion of the target. The foregoing serves to degrade the performance of the x-ray generator, and thus the performance of the well logging instrument utilizing the x-ray generator.
As such, further advances in the area of electron accelerators for x-ray generators are desirable. It is desired for such new electron accelerators to reduce the buildup of undesirable conductive particles on insulating surfaces, and thus provide a high degree of stability and consistency, such that they can deliver a tightly focused electron beam to the target and consistently generate the desired x-ray photons.